However: after installing/flashing TWRP you will notice you can't get past the start screen.
Why: touch doesn't work in the newest TWRP on MIX (and some other devices)
Workaround: for some an otg usb mouse might work. For me, it does not work. (while it does work on a running system / phone itself)

So basically: You are stuck. Like me.

Can't update, have been googling for a patched TWRP but alas. No solution avaible.